This invention relates to a frame for motorcycles, and more particularly to a frame for motorcycles equipped with water-cooled engines.
Conventionally, in a motorcycle equipped with a water-cooled engine, the engine is supportedly mounted on a pair of left and right down tubes extending substantially vertically downward from a front portion of the main frame and then extending rearwardly of the motorcycle, and a radiator for cooling engine cooling water is supportedly mounted on the vertically downwardly extending portion of the down tubes. It is hard to mount the engine and many parts related to the engine into a small space defined between the main frame and the down tubes. To facilitate the operation of mounting and dismounting the engine, etc. into and out of the above space, a frame has been proposed in which one of the left and right down tubes is separable from the main frame.
However, in motorcycles equipped with water-cooled engines, it is widely employed to connect the radiator, the engine and a cooling water pump in a direct manner by means of india-rubber hoses or the like. The operation of laying the hoses in the narrow space enclosed by the main frame and the down tubes is troublesome and painful, which still makes harder the operation of mounting the engine, the radiator, etc. onto the frame, even with the above-mentioned separable down tube. Furthermore, the connection of the radiator, the engine and the water pump requires a considerable number of mounting parts.
Moreover, the above separable frame member should have sufficient structural strength enough to withstand use as a component member of the support frame of the motorcycle. Particularly, the joints between the separable frame member and the main frame should be sufficiently firm to obtain sufficient structural strength of the overall frame.